The invention relates to an automatic calender which eliminates the need for adjustment over a prolonged period of time. Calendar clocks are well known themselves since long, including both mechanical and electrical types. However, an automatic calendar which is compact and easily manoeuvrable without requiring adjustment over a prolonged period of time is not yet available. In a mechanical clock, a definite, regular circulation prevails in the carry from seconds digit to minute digit or from minute digit to hour digit, so that the construction and assembly of gear trains and carry propagation has been relatively simple. However, in the day mechanism section of the mechanical calendar, while a decimal carry system can be employed when progressing from 1st day to 31st day, there is an irregular carry at the end of the month, changing from 31st to 1st day. In order to provide a definite circulating operation for the carry which permits a change from 31st to 1st day, there have been various proposals including using a scale of 31 system for the dating mechanism of the calendar, using a technique in which the date proceeds from 31 to 32, 33 . . . 39, 00, 01 and in which the intermediate days are skipped to make the next step from 31 to 01, or the use of a cam, lever, pin or the like to change the tens' day digit through the carry so that 1st day may be displayed. Except for the day digits, the arrangement for the gear train and carry propagation can be achieved in a relatively simple manner in a mechanical calendar mechanism since twelve months provide a carry to the year digit and there is a definite circulation in the year digit in a period of four years from one leap year to the next. Similarly, in an electrical calendar mechanism having an automated day display, there is a program available at the end of the month which has a period of four years or 1461 days from one leap year to the next. Thus, if it is possible to provide a regular operation in a simple manner when changing from 31st to 1st day when producing a carry to the month digit, there can be established, by incorporating cams or contacts together with gate or switching circuits, a progress over 1461 days whereby the change of dating from the end of the month to the first day of the next month can automatically be achieved, including such change at the end of a short month. However, the use of a scale of 31 system for the dating involves an increased number of numerals to be displayed to result in an enlarged mechanism. While a drum display is proposed to provide a compact structure for such mechanism, the resulting angular displacement per day becomes small, thus requiring a special arrangement for the carry propagation. While a decimal system provides a compact structure for the display of days, it involves difficulties with the irregular carry at the end of the month.